Carbon nanotubes (CNTs) consist of graphene sheets of carbon atoms which are rolled up into a cylinder having a diameter in the range of nanometers and a length which may range from nanometer to centimeters. CNTs may be so-called single-walled nanotubes (SWNT) having a structure of a uniform cylinder of a single graphene sheet. Alternatively, CNTs may be so-called multi-walled nanotubes (MWNT) consisting of a plurality of SWNTs with different diameter and thus arranged within each other, or a single graphene sheet which is rolled up around itself several times giving multiple layers.
Several methods for the production of CNTs are known, including, for example, arc discharge, laser ablation, and chemical vapor deposition (CVD), wherein the latter is the most common for commercial production of CNTs and typically involves preparing a substrate with a metal catalyst, such as, iron, cobalt or nickel and subsequently heating the substrate in an atmosphere comprising a process gas such as ammonia, nitrogen or hydrogen, and a gas comprising a carbon source, such as for example acetylene, ethylene, or alcohols. Thus, giving growth of CNTs at the surface of the metal catalyst. The orientation of the CNTs on the metal catalyst may be controlled by adapting the reaction conditions such that vertically aligned CNTs are produced, i.e. CNTs extending perpendicularly to the surface of the metal catalyst.
Given that CNTs have high mechanical strength as well as high thermal and electrical conductivity, many potential applications for CNTs have been proposed, including, for example, sensors, hydrogen storage media, probes, semiconductor device, field emission device, and conductive and high-strength composites, among others.
A problem associated with present conventional manufacturing methods for CNTs is that it is difficult to control both the growth of CNTs in predefined orientations and configurations at specific location on a substrate and the interface with other materials such as metal electrodes.
U.S. Pat. No. 6,900,580 B2 discloses a field emission device and the manufacturing of such device, wherein the device has bundles of aligned parallel CNTs on a substrate, the bundles extending only from regions of the substrate patterned with a catalyst material, thus providing accurate control of size, shape, and distribution of the bundles on the substrate surface, and furthermore, each bundle can thereby be individually controlled by connecting patterned metallization lines to the bundles.
However, the method for manufacturing of CNTs according to U.S. Pat. No. 6,900,580 B2 is tedious and presumably not very cost effective.
Hence, there is a need in the art to facilitate the manufacturing of CNTs for use in electrical devices.